The work outlined in this research project is directed toward the study of the process of excitation of hair-cell systems, especially in the cochlea. Experiments are planned to test and improve current theories of electromechanical transduction on the organ of Corti, and to ascertain the role of the cochlear microphonics (CM) and summating potentials (SP) in the excitatory processes of the VIIIth nerve fibers. This will be accomplished by simultaneously recording the cochlear potential and the neural responses of single fibers before and after experimental modification of the cochlear potentials. Comparative studies will be made on the lateral-line system of the toad Xenopus laevis. The differential sensitivity of the system to changes in pressure and displacement of water will be studied to identify the adequate mechanical stimuli. The adequacy of the electromechanical hypothesis for the function of the hair cells in the lateral line will be tested by studying the effect of electrical polarization on the neural responses elicited simultaneously and independently of mechanical stimulation.